Baffles for agitated vessels



Dec. 3, 1968 JLJNG ET Al.

BAFFLES I FOR AGITATED VESSELS Filed May 18, 1967 INVENTORS: H A N S J U N G WALTER Z A P F W MW United States Patent 0 3,414,240 BAFFLES FOR AGITATED VESSELS Hans Jung and Walter Zapf, Ludwigshafen (Rhine), Germany, assignors to Badische Anilin- & Soda-Fabrik Aktiengesellschaft, Ludwigshafen (Rhine), Germany Filed May 18, 1967, Ser. No. 639,431 Claims priority, application Germany, May 21, 1966, B 87,229 2 Claims. (Cl. 259-107) ABSTRACT OF THE DISCLOSURE Bafiles for agitated vessels provided with a motordriven impeller which comprise a stationary support member parallel to the stirrer and two rows of vanes mounted radially on the support member.

This invention relates to means for disturbing the flow of a liquid in an agitated vessel wherein the liquid rotates about a vertical axis, forming a so-called forced vortex. The free surface of the liquid becomes curved according to the centripetal acceleration, the inertia and the pressure within the fluid.

An impeller in a stirred vessel in general produces not only a turbulent motion of the liquid contents of the vessel, but also a rotation of the body of liquid about the axis of the impeller or about the central axis of the container. As a result the surface of the liquid becomes curved, i.e. it sinks in the middle and rises at the edge, thus forming a vortex.

One of the objects of bafiles in stirred vessels is the suppression of these vortices formed by centrifugal force. In the case of a baflle of conventional design the tangential speed of the liquid is decreased by stationary fingers, plates or other insertions acting as obstructions. A von Karman vortex street forms behind the baffle which results in eddies having local strong shear gradients. This behavior of the liquid behind the baffle gives dead spaces without movement in which the fluid often coagulates.

The object of this invention is to avoid this disadvantage and to provide a baffie for a stirred vessel equipped with an impeller which suppresses the vortex generally formed in the liquid without disturbing the flow as a whole or increasing the power required for driving the impeller. The baflle according to this invention comprises a stationary support member which is located parallel to the impeller shaft and has a streamlined cross section and two rows of vanes mounted radially on opposite sides of the support member, the vanes facing the impeller shaft being arranged at an angle of 1I+oc to the horizontal and the vanes facing the wall of the vessel being arranged at an angle of a to the horizontal.

To adapt the angle of the individual vanes to different liquid speeds, the individual vanes are rotatable about a horizontal axis so that the angle of incidence may be changed; means are provided within the support member (which is made hollow for this purpose) for the simultaneous rotation of the two rows of vanes.

The support member and the vanes may also be used at the same time for the transfer of heat. For this purpose, in a further embodiment of the bafile according to this invention, the support member and the individual vanes are made hollow and means for supplying a heattransfer medium to the vanes and withdrawing it from them may be provided.

The invention will now be described with reference to the accompanying drawings. FIGURES 1a and 1b are elevations at right angles of the bafile; FIGURE 2 is an elevation, FIGURE 3 is a plan view on an enlarged scale 3,414,240 Patented Dec. 3, 1968 ice of the bathe and FIGURE 4 is a sectional elevation of a filled stirred vessel provided with an impeller, the lefthand half of the figure showing the surface of the liquid when a bafile according to this invention is used and the right-hand half showing the surface which is formed when a baffle is not employed.

The battle (FIGURE 1) consists of a support member 1 which has a streamlined cross section to minimise flow resistance. Two rows 2, 3 of vanes 2a, 3a are mounted on the support member transversely to its axis (FIG- URES 2 and 3). The support member 1 with the rows of vanes 2 and 3 is located parallel to the axis of the impeller shaft 4 between the wall 5 of the stirred vessel and the shaft 4.

The vanes are arranged at an angle to the horizontal on the support member 1, row 2 at an angle of +11 and row 3 at an angle of a to the horizontal. In this way the level of the liquid in the stirred vessel is raised in the vicinity of the impeller shaft 4 and lowered at the wall 5. The tangential speed of the liquid is thus decreased by the bafile which deflects the flow.

FIGURE 4 illustrates the effect of the bafile according to this invention on the vortex in a vessel having a capacity of 1 cu. m. The profile line 6 (FIGURE 4, righthand side) of the vortex is raised at the center and lowered at the wall of the vessel after the baffle has been inserted (FIGURE 4, left-hand side).

When a baffle of this type is installed in an agitated vessel used for dispersion polymerization, it is found that the vanes, due to the high speed of flow, remain free from coagulate. The free oscillation of conventional bafiles produced by the trail of vortices cannot be observed. The amount of energy to be supplied by the impeller is considerably less at the same number of revolutions.

Measurements showed that:

N is the power consumption of the impeller motor when a baflle is not employed;

N is the power consumption with a bafile according to this invention; and

N is the power consumption with a fingers-type baflie of conventional design.

Measurements in the vortex showed that:

V :V :V =1:0.2:0.6

where:

V, is the volume of the vorter when a baffie is not employed;

V is the volume of the vortex when a bafile according to this invention is used; and

V is the volume of the vortex when a finger-type bafile of conventional design is used.

Moreover, experiments have shown that the vortex can also be effectively influenced by vanes of simple geometric shape, for example plates, which are arranged at angles of +a and a to the horizontal.

If the baffle is to be used in a stirred vessel in which different materials will be mixed at different speeds of rotation, the individual vanes are advantageously adjustably mounted. The series of vanes can then be rotated to the right or left through the hollow support member.

When it is desired to cool or heat the contents of the vessel, it is advantageous to make the support member and in some cases also the individual vanes hollow. A heat-transfer medium for the supply or withdrawal of heat can then be passed through the hollow support member.

3 4 We claim: 2. A bafile as claimed in claim 1 wherein the vanes 1. A 'bafiie for a stirred vessel provided with an imhave astreamlined cross section, peller which comprises a stationary support member having a streamlined cross section and arranged Within the References Cited stirred vessel with its axis parallel to that of the impeller 5 UNITED STATES PATENTS shaft and two rows of vanes mounted on opposite sides of the support member radially to the axis thereof, the 2,108,482 2/1938 Greene 259 107 vanes facing the impeller haft being at an angle of at- 2,159,856 5/ 1939 MacLean 259107 tack of +a to the horizontal and the vanes facing the wall 3,265,368 3/1966 Nocera 259-108 of the vessel bein at an an le of attack f to the horiz g 0 a 10 ROBERT w. JENKINS, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,414,240 December 3, 1968 Hans Jung et a1.

It is certified that error appears in the above identified petent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 53, "v+a" should read +0 Signed and sealed this 28th day of April 1970.

(SEAL) Attest:

Edward M. Fletcher, Jr. WILLIAM E. SCHUYLER, JR.

Attesting Officer Commissioner of Patents 

